Method and apparatus for channel quality estimation in consideration of interference control and coordinated communication in cellular system

ABSTRACT

Disclosed are a method and an apparatus for channel quality estimation in consideration of interference control and coordinated communication in a cellular system. A base station receives an SRS transmitted by a terminal to thus measure received power, and then configures, for the terminal, a CSI process which may measure SINRs for base stations having higher SRS received power. If the terminal feeds back, to the base station, channel quality information for the configured CSI process, the base station determines an SINR and a MCS to be applied to data transmission in consideration of a received CQI and a CoMP transmission scheme, and applies the determined SINR and MCS to thus transmit data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/508,907which is the 371 National Stage of International Application No.PCT/KR2015/009325, filed Sep. 3, 2015, which claims priority to KoreanApplication No. 10-2014-0116850, filed Sep. 3, 2014, the disclosures ofwhich are incorporated herein by reference into the present disclosureas if fully set forth herein.

BACKGROUND 1. Field

The present invention relates to a method and apparatus for determininga channel quality estimation scheme in a broadband wirelesscommunication system.

2. Description of Related Art

The mobile communication system has been developed for the user tocommunicate on the move. With the rapid advance of technologies, themobile communication system has evolved to a level capable of providinga high speed data communication service as well as a voice telephonyservice.

Recently, as one of the next generation mobile communication systems,LTE-Advanced (LTE-A) is being standardized by the 3rd GenerationPartnership Project (3GPP). The LTE-A is a continuously evolvingtechnology for realizing high-speed packet-based communication at a datarate of 3 to 10 times higher than that of current systems.

LTE-A adopts Coordinated Multi-Point (CoMP) transmission/reception as acommunication scheme in which neighboring base stations transmit/receivedata based on the channel information provided by a terminal in a way ofcooperation and interference control, thereby reducing inter-basestation interference and improving the data rate of the terminal in anoptimal communication environment.

Although the coverage of base stations participating in a CoMPtransmission is restricted to the cells of one evolved Node B (eNB) inan LTE-A Release 11 standard system, the present invention is applicableto systems supporting the inter-eNB CoMP transmission as well as thesystems following the CoMP transmission scenarios defined in the LTE-Arelease 11 standards. In the following description, the term “basestation” is used in the meaning of coverage including the cellsbelonging to one or more eNBs or base stations specified for othercommunication systems. For this reason, drawings are depicted as normaldiagrams without boundaries between inside and outside of eNBs.

In the following description, the term “LTE system” is used with themeaning to include legacy LTE and LTE-A systems.

SUMMARY

In order to support the CoMP operation, it is necessary to define a CSIprocess for a terminal to perform feedback of channel status informationfor use in the CoMP operation. LTE-A specifies support for up to 4 CSIprocesses, which are restrictive to secure rich channel statusinformation; thus, there is a need of a method for acquiring channelstatus information related to the neighboring base stations efficientlyusing the limited number of CSI processes.

In accordance with an aspect of the present invention, a method fortransmitting channel quality information (CQI) from a terminal to a basestation in a wireless communication system includes transmitting, at theterminal, a sounding reference signal and receiving channel statusinformation (CSI) configuration information configured based on a resultof comparing reception powers of the sounding reference signal at aserving base station and neighboring base stations.

In accordance with another aspect of the present invention, a method fora base station to receive Channel Quality Information (CQI) from aterminal in a wireless communication system includes receiving asounding reference signal from the terminal, receiving soundingreference signal-reception power information from neighboring basestations, generating channel status information (CSI) configurationinformation by comparing reception powers of the sounding referencesignal at a serving base station and neighboring base stations, andtransmitting CSI configuration information to the terminal.

In accordance with another aspect of the present invention, a terminalfor transmitting channel quality information (CQI) to base stations in awireless communication system includes a transceiver for transmittingand receiving signals and a control unit which controls the transceiverto transmit a sounding reference signal and receive channel statusinformation (CSI) configuration information configured based on a resultof comparing reception powers of the sounding reference signal at aserving base station and neighboring base stations.

In accordance with still another aspect of the present invention, a basestation for receiving channel quality information (CQI) from a terminalin a wireless communication system includes a transceiver fortransmitting and receiving signals and a control unit which controls thetransceiver to receive a sounding reference signal from the terminal andsounding reference signal-reception power information from neighboringbase stations, generates channel status information (CSI) configurationinformation by comparing reception powers of the sounding referencesignal at a serving base station and neighboring base stations, andcontrols the transceiver to transmit CSI configuration information tothe terminal.

The channel quality estimation method of the present invention for usein a broadband communication cellular system is advantageous in terms offacilitating data transmission by estimating channel quality with alimited number of CSI processes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a signal flow diagram illustrating a procedure for measuringand applying channel quality information in a general communicationsystem;

FIG. 2 is a diagram illustrating an exemplary communication situationbetween a UE and an eNB in a cellular communication system;

FIGS. 3A-3D are diagrams illustrating communication situations forrespective CSI processes of Table 2;

FIG. 4 is a flowchart illustrating a procedure for a UE to measuremultiple SINRs for feedback;

FIG. 5 is a flowchart illustrating the overall operation of the presentinvention;

FIG. 6 is a diagram illustrating an SRS transmitted from a UE to eNBs;

FIG. 7 is a block diagram illustrating an eNB controlling the CoMPtransmission operation; and

FIG. 8 is a block diagram illustrating an eNB and a CoMP management unitthat is implemented as a separate device for controlling the CoMPtransmission operation.

DETAILED DESCRIPTION

Exemplary embodiments of the present invention are described in detailwith reference to the accompanying drawings. Detailed descriptions ofwell-known functions and structures incorporated herein may be omittedto avoid obscuring the subject matter of the present invention. Further,the following terms are defined in consideration of the functionality inthe present invention, and they may vary according to the intention of auser or an operator, usage, etc. Therefore, the definition should bemade on the basis of the overall content of the present specification.

Although the description is directed to the OFDM-based radiocommunication system, particularly the 3GPP LTE, it will be understoodby those skilled in the art that the present invention can be appliedeven to other communication systems having a similar technicalbackground and channel format, with a slight modification, withoutdeparting from the spirit and scope of the present invention.

FIG. 1 is a signal flow diagram illustrating a procedure for measuringand applying channel quality information in a general communicationsystem.

In reference to FIG. 1, the eNB 110 acts as s transmitter to transmitdownlink signals to the UE 100, the downlink signals including a pilotsignal for use in channel quality measurement at step 120. The UEmeasures channel quality with the pilot signal at step 130 and transmitsmeasured channel quality information to the eNB at step 140. A schedulerof the eNB performs scheduling at step 150 to allocate radio resourcesto the UE based on the channel quality information.

The eNB may allocate the radio resources in a way of acquiringefficiently much information on the channel quality between the eNB andthe UE. If the eNB can acquire information on the interference fromneighboring eNBs as well as the signal from the serving eNB to the UE,it may perform signal transmission in a way of 1) protecting againstinfluence from the neighboring eNB causing strong interference or 2)adjusting a resource allocation amount based on the serving eNB and theaggressor eNB. The more channel information the UE reports, the morethroughput improvement the wireless communication system will achieve.

For this purpose, the 3GPP LTE-A Release 11 has adopted a datacommunication technology for a UE to communicate data with multiple eNBsin a cooperative and interference-control manner based on the channelstatus information measured in association with the multiple eNBs, socalled CoMP. In LTE-A, three CoMP schemes have been discussed.

First, Joint Transmission (JT) is a technique for one or more eNBs astransmitters share the data destined for a UE in advance and transmitthe data to the UE in a cooperative manner. The main gain of this schemeis a combining gain achieved by receiving data from one or more eNBssimultaneously. Second, Coordinated Scheduling/Coordinated Beamforming(CS/CB) is a technique of selecting an eNB for communication based onthe channel status information between the UE and multiple eNBs tominimize interference from neighboring eNBs through interference controlor beamforming without sharing data destined to the UE among the eNBs.The main gain of this scheme is an interference control gain capable ofadjusting interference amount by controlling signal transmissions of theeNBs. Third, Dynamic Point Selection (DPS) is a technique in which aneNB having the best channel condition, among multiple eNBs sharing thedata destined for a UE, transmits data to the UE, the best eNB beingselected at a short interval. The main gain of this scheme is selectiondiversity capable of selecting the eNB guaranteeing the best receptionperformance of the UE among the eNBs.

In order to support the three CoMP schemes described above, it isnecessary for channel status information feedback operations of the UEto be defined for respective CoMP schemes. For this purpose, the 3GPPLTE standard specifies channel status information feedback schemes asfollows.

An eNB configures two types of radio resources for channel measurement,i.e., Channel State Information-Reference Signal (CSI-RS) andCSI-Interference Measurement (CSI-IM), in order for a UE to performchannel measurements for one or more eNBs including itself. First, theUE may detect signal components from a combination of up to 3neighboring eNBs using a non-zero power CSI-RS on the CSI-RS resource.Second, the UE may detect interference components from a combination ofup to 3 neighboring eNBs using zero power CSI-RS on the CSI-IM resource.For this purpose, the eNBs participating in the CoMP transmissiontransmit signals on the radio resources designated through CSI-RS andCSI-IM configurations as intended by the serving eNB.

The UE may measure a Signal-to-Interference-plus-Noise Ratio (SINR)through up to 4 CSI processes per component carrier combining a total of6 measurement results and perform feedback of Channel QualityInformation (CQI) generated in consideration of presence/absence ofinterference from the neighboring eNBs to the serving eNB.

The eNB can acquire channel quality information required for CoMPtransmission operations such as JT, CS/CB, and DPS by configuring theCSI-RS and CSI-IM appropriately.

FIG. 2 is a diagram illustrating an exemplary communication situationbetween a UE and an eNB in a cellular communication system.

In reference to FIG. 2, assuming that there is a UE 200, an eNB A 210serving the UE 200 as denoted by 211, and neighboring eNBs B, C, and D220, 230, and 240, the signals 221, 231, and 241 transmitted by theneighboring eNBs B, C, and D are regarded as interference signals. TheUE may detect up to three signal and interference components includingthe signal from the serving eNB A. For the CS/CB scheme, referencesignals may be configured as shown in Table 1.

TABLE 1 Signal component Interference component CSI-RS eNB signal CSI-IMeNB signal configuration transmission on configuration transmission onindex CSI-RS resource index CSI-IM resource CSI-RS cfg. 0 Transmissionat eNB A CSI-IM cfg. 0 Mute at eNB A CSI-RS cfg. 1 Transmission at eNB BCSI-IM cfg. 1 Mute at eNB B CSI-RS cfg. 2 Transmission at eNBs CSI-IMcfg. 2 Mute at eNBs A A and B and B

Each item indicates a CSI-RS configuration or a CSI-IM configuration.

By combining the signal and interference components, it is possible toconfigure a CSI process for the combination of eNBs A and B as follows.

TABLE 2 CSI process Combination of CSI processes SINR combination CSIprocess 0 CSI-RS cfg. 0/CSI-IM cfg. 0 $\frac{A}{B + {NI}}$ CSI process 1CSI-RS cfg. 0/CSI-IM cfg. 2 $\frac{A}{NI}$ CSI process 2 CSI-RS cfg.1/CSI-IM cfg. 1 $\frac{B}{A + {NI}}$ CSI process 3 CSI-RS cfg. 1/CSI-IMcfg. 2 $\frac{B}{NI}$

In Table 2, NI denotes the sum of interferences and noises from the eNBsC and D. If the UE transmits the combinations to the eNB, the eNB checksreception SINR information of the UE for four cases as follows.

FIGS. 3A-3D are diagrams illustrating communication situations for therespective CSI processes of Table 2. In reference to Table 2, FIG. 3Ashows CSI process 0, FIG. 3B shows CSI process 1, FIG. 3C shows CSIprocess 2, and FIG. 3D shows CSI process 3. FIG. 3A is directed to a CSIprocess of a UE 300 served by the eNB A 301 for processing thecombination of the signal component CSI-RS cfg. 0 transmitted by the eNBA 301 and the sum of the signal from the eNB B 302 and interference andnoise components CSI-IM cfg.0 from the eNB C 303 and eNB D 304. FIG. 3Bis directed to a CSI process of the UE 310 served by the eNB A 311 forprocessing the combination of the signal component CSI-RS cfg. 0 fromthe eNB A 311 and the sum of interference and noise components CSI-IMcfg. 2 from the eNB C 313 and eNB D 314. FIG. 3C is directed to a CSIprocess of the UE 320 served by the eNB B 322 for processing thecombination of the signal component CSI-RS cfg. 1 transmitted by the eNBB 322 and the sum of the signal component from the eNB A 321 andinterference and noise components CSI-IM cfg. 1 from the eNBs C 323 andeNB D 324. FIG. 3D is directed to a CSI process of a UE 330 served bythe eNB B 332 for processing the signal component CSI-RS cfg. 1 and thesum of the interference and noise components CSI-IM cfg. 2 from the eNBC 333 and eNB D 334. In the cases of CSI processes 2 and 3, the UE isactually served by the eNB A; but, assuming that the eNB B is servingthe UE, the CSI processes are configured for measuring the SINR. The UEmeasures the SINR for four cases of FIGS. 3A-3D through the configuredCSI processes and transmits the measurement result to the eNB in theform of CQI.

In the case of configuring a CSI process for JT or DPS rather thanCS/CB, it may be possible to perform CSI process configuration as shownin Table 4 based on the CSI-RS and CSI-IM configurations of Table 3 forJT and as shown in Table 6 based on the CSI-RS and CSI-IM configurationsof Table 5 for DPS.

TABLE 3 Signal component Interference component CSI-RS eNB signal CSI-IMeNB signal configuration transmission on configuration transmission onindex CSI-RS resource index CSI-IM resource CSI-RS cfg. 0 Transmissionat CSI-IM cfg. 0 Transmission at eNBs A and B eNBs C and D CSI-RS cfg. 1Transmission at CSI-IM cfg. 1 Transmission at eNBs A and C eNBs B and DCSI-RS cfg. 2 Transmission at CSI-IM cfg. 2 Transmission at eNBs A and DeNBs B and C

TABLE 4 Combination of SINR CSI process CSI processes combination CSIprocess 0 (JT of A and B) CSI-RS cfg. 0/ CSI-IM cfg. 0$\frac{A + B}{C + D + N}$ CSI process 1 (JT of A and C) CSI-RS cfg. 1/CSI-IM cfg. 1 $\frac{A + C}{B + D + N}$ CSI process 2 (JT of A and D)CSI-RS cfg. 2/ CSI-IM cfg. 2 $\frac{A + D}{B + C + N}$ CSI process 3(reserved)

TABLE 5 Signal component Interference component CSI-RS eNB signal CSI-IMeNB signal configuration transmission on configuration transmission onindex CSI-RS resource index CSI-IM resource CSI-RS cfg. 0 Transmissionat CSI-IM cfg. 0 Transmission at eNB A eNBs B, C, and D CSI-RS cfg. 1Transmission at CSI-IM cfg. 1 Transmission at eNB B eNBs A, C, and DCSI-RS cfg. 2 Transmission at CSI-IM cfg. 2 Transmission at eNB C eNBsA, B, and D

TABLE 6 Combination of SINR CSI process CSI processes conversion CSIprocess 0 CSI-RS cfg. 0/ CSI-IM cfg. 0 $\frac{A}{B + C + D + N}$ CSIprocess 1 CSI-RS cfg. 1/ CSI-IM cfg. 1 $\frac{B}{A + C + D + N}$ CSIprocess 2 CSI-RS cfg. 2/ CSI-IM cfg. 2 $\frac{C}{A + B + D + N}$ CSIprocess 3 (reserved)

In the SINR formula, N denotes noise.

Using Tables 3 and 4, it is possible to configure a CSI process for JT,i.e., acquire SINR information for cooperative transmission of two ormore eNBs, or for DPS, i.e., acquire per-eNB SINRs to select an eNB withthe best channel status in the transmission point selection process.

The eNB selects a scenario maximizing the throughput of the UE andcontrols data transmission based on the channel quality informationfeedback from the UE. In the case where multiple UEs exists in thecommunication network, the eNB receives channel quality informationthrough one or more CSI processes per UE and performs scheduling and eNBselection based on the channel quality information in a way ofoptimizing network throughput.

Configuring multiple CSI processes is advantageous in that the servingeNB can receive information on the influence of neighboring eNBsdirectly from the UE, but it has a drawback in that the number of CSI-RSand CSI-IM configurations is limited to 3 and the number of CSIprocesses to 4. A UE may be influenced by at least 7 closest eNBsincluding the serving eNB in a hexagonal cell model, and the number ofeNBs influencing the UE is likely to increase in the real communicationsystem in which the cells are sectored. In the case that there are alarge number of eNBs influencing the UE, it may be impossible to performmeasurement on the signals from all the eNBs completely with the CSIprocess configurations specified in the standard.

Although CSI-RS and CSI-IM resources are configured per set of specificeNBs, the channel quality information capable of being acquired, i.e.,SINR combinations, is limited by the number of CSI-RS processes, i.e.,4, and it is impossible to achieve the goal of securing various SINRvalues associated with neighboring eNBs.

In the example of CS/CB, if a CSI process is configured to select two offour eNBs for simultaneous transmission or alternative transmission, thetotal number of configurable cases becomes 24 (4 combination 2×4). Thatis, it becomes possible to select a combination of eNBs that promise thebest performance of the UE based on the 24 SINRs. This means that it isnecessary to configure a CSI process, changing the combination of eNBs 6times, to receive feedback from the UE sequentially because the numberof combinations of SINRs that can be configured simultaneously is 4.

FIG. 4 is a flowchart illustrating a procedure for a UE to measuremultiple SINRs for feedback. The eNB configures candidate eNBs for SINRmeasurement at step 400 and transmits to the UE a CSI-RS configuration,a CSI-IM configuration, and a CSI process combination through RadioResource Control (RRC) signaling at step 410. The UE performs CQImeasurement per CSI process according to the information from the eNB atstep 420 and performs feedback of 4 CQIs to the eNB at step 430. Thisprocedure is repeated by changing the candidate eNB combination at step440.

As shown in FIG. 4, it is necessary for the UE to determine repeatedlychannel quality based on the configuration information transmitted bythe eNB through RRC signaling and to perform repeatedly CQI feedback inorder for the eNB to acquire a total of 24 CQIs. The frequent RRCconfiguration information transmission from the eNB to the UE causes adownlink overhead problem, the frequent CQI transmission from the UE tothe eNB causes an uplink overhead problem, and the frequent change ofCQI elongates the CQI transmission interval for the same eNBcombination, resulting in an increase of the probability of a mismatchbetween the channel status at the instant when the UE transmits data onthe resources allocated by the eNB under the assumption of the best datatransmission condition and the channel status indicated by the CQIfeedback from the UE. Configuring 24 CSI processes for SINR measurementis the case of assuming the existence of only 4 eNBs around the UE;however, in the real network environment, there are likely to be moreeNBs around the UE and thus the number of cases for correct measurementincreases exponentially. This means that the aforementioned problemsbecome worse.

The above problems are caused by applying the CQI-related downlinksignaling specified in the standard, i.e., only the RRC signaling andchannel quality information feedback, to a situation requiring aplurality of CSI process configurations and operations. There istherefore a need of a method for estimating channel quality efficientlywithout compromising the advantage in terms of measurement ofinterference from neighboring eNBs as a goal of the introduction ofmultiple CSI processes.

The present invention is directed to a method for determining the SINRfor use in downlink data transmission in consideration of a CoMPtransmission scheme using the channel quality information fed backthrough a plurality of CSI processes configured based on ReferenceSignal Received Power (RSRP) included in the measurement report of theUE, as a UE-eNB (in the present invention, an eNB can be interpreted asa Transmission Point (TP) or a Remote Radio Head (RRH)) channelinformation or uplink Sounding Reference Signal (SRS) information.

FIG. 5 is a flowchart illustrating the overall operation of the presentinvention. The UE transmits an SRS in uplink at step 500 and, uponreceipt of the SRS, the eNB measures a received signal power of the SRSand shares the SRS received signal power with other eNBs at step 510.The eNB prioritizes the SRSs in a descending order of reception power atstep 520 and configures three CSI-RSs and three CSI-IMs to N eNBs withthe highest SRS reception powers at step 530. The eNB configures 4 CSIprocesses by combining the CSI-RS configurations and CSI-IMconfigurations and, at step 550, transmits to the UE the information onthe CSI-RS configurations, CSI-IM configurations, and combined CSIprocesses through RRC signaling. The UE measures the SINR based on theCSI processes to generate CQIs and perform CQI feedback at step 560; andthe eNB calculates at step 570 an SINR for data transmission based onthe received CQI and the CoMP transmission scheme to be used, determinesa Modulation and Coding Scheme (MCS) for data transmission at step 580,and transmits downlink data to the UE using the MCS at step 590. Adescription is made of the invention in detail hereinafter.

In the following description, it is assumed that uplink SRS is used asUE-eNB channel information for configuring multiple CSI processes. Theuplink SRS is a signal transmitted by the UE for use by the eNB inmeasuring uplink channel quality. Since the eNB has the information onthe transmission power of the UE, it may be possible to estimate thechannel quality between the UE and the eNB by estimating the signalattenuation amount while the SRS propagates the channel.

In a Time Division Duplex (TDD) mode, since the uplink for SRStransmission and the downlink for data transmission are reciprocal onthe same frequency, it may be possible to use the uplink channel qualityestimated based on the SRS as downlink channel quality. In a FrequencyDivision Duplex (FDD) mode, since the uplink and downlink are ondifferent frequencies with different channel characteristics, it may beunreasonable to use the uplink channel quality estimated based on theSRS for downlink transmission directly, but it may be used indirectlyfor relative comparison of channel quality.

FIG. 6 is a diagram illustrating an SRS transmitted from a UE to eNBs.The SRS transmitted by the UE 600 may be received by the neighboringeNBs (i.e., eNB B 620, eNB C 630, and eNB D 640) as well as the eNB A610 serving the UE 600. Here, it is assumed that the eNBs share thePhysical Cell Identifier (PCID) and the SRS resource allocationinformation of the serving eNB A so as to measure SRS reception powerbased thereon.

A certain processor sorts the eNBs in a descending order of theSRS-received signal powers. The processor may be located inside an eNBor be a separate device. If the eNBs are sorted in the descending orderof eNB A>eNB B>eNB C>eNB D, each eNB may sort the interferenceaggressors in an order of interference strength, and this order may beused as a descending order of interference aggressors to the UE indownlink transmission directly in the TDD mode or indirectly in the FDDmode.

The present invention includes a method for configuring CSI-RS andCSI-IM configurations and multiple CSI processes based on theSRS-reception power order. This method includes 1) selecting N highestSRS reception powers, 2) configuring up to 3 CSI-RS configurations basedon the N eNBs corresponding to the N highest SRS-reception powers, and3) configuring up to 3 CSI-IM configurations based on the N eNBscorresponding to the N highest SRS-reception powers. In comparison withthe operation without use of SRS, since only the N eNBs with highSRS-reception powers are regarded as CSI process configuration targets,it is possible to increase the probability of selecting neighboring eNBsthat are likely to actually cause interference to the UE and, althoughthere are many eNBs around the UE, the number of eNBs to be selected islimited to N, thereby protecting against an increase of CQI acquisitioncomplexity. Since there is no need, unless the location of the UE ischanged abruptly, for the UE to continue correcting the CSI-RS, CSI-IM,and CSI process configuration information and transmitting them throughRRC signaling and the eNB receives the uplink SRS periodically, thismethod is advantageous in terms of causing no extra overhead. Here, H isa system parameter that can be optionally configured and shared amongeNBs.

The eNB transmits to the UE the information on the CSI-RS, CSI-IM, andCSI-RS process configurations configured as described above.

A description is made hereinafter of the method for generating SINRvalues for use in downlink data transmission according to a CoMPtransmission scheme based on the CQI feedback from a UE.

The eNB selects three eNBs with the highest SRS-reception powers. It isassumed that the eNB can receive CQIs from the UE according to three CSIprocesses. If the eNBs are sorted in the descending order of eNB A>eNBB>eNB C>eNB D according to the SRS-reception power and if the UE isserved by the eNB A, the eNB selects the eNB A serving the UE, the eNBB, and the eNB C. In this case, CSI-RS and CSI-IM configurations areconfigured as shown in Table 5.

TABLE 7 CSI-RS/CSI-IM eNB signal transmission on configuration indexconfigured CSI-RS resource CSI-RS configuration CSI-RS cfg. 0Transmission at eNB A CSI-RS cfg. 1 Transmission at eNB B CSI-RS cfg. 2Transmission at eNB C CSI-IM configuration CSI-IM cfg. 0 Transmission atall eNBs

In the case, the CSI process is configured as shown in Table 8 based onTable 7.

TABLE 8 CSI process CSI process configuration SINR conversion CSIprocess 0 CSI-RS cfg. 0/ CSI-IM cfg. 0$\frac{A}{\left( {A + B + C + {NI}} \right)/\alpha} = X$ CSI process 1CSI-RS cfg. 1/ CSI-IM cfg. 0$\frac{B}{\left( {A + B + C + {NI}} \right)/\alpha} = Y$ CSI process 2CSI-RS cfg. 2/ CSI-IM cfg. 0$\frac{C}{\left( {A + B + C + {NI}} \right)/\alpha} = Z$

In the SINR conversion formulas in Table 8, a is an essential factorthat causes a side effect of always making the actually measured SINRbecome less than 1 because all signals are transmitted simultaneouslyaccording to the CSI-IM configuration. This means that the CQI derivedfrom the measured SINR always has a small value, resulting in reductionof distinctiveness. Accordingly, when all the eNBs transmit referencesignals at the Resource Elements (REs) to which CSI-IM is mappedaccording to the CSI-IM configuration, power reduction (deboosting) isperformed by as much as the amount indicated by a. The system parameterα is optionally configured and shared among eNBs

In particular, the system parameter α may be applied in aninterference-limited environment. In an interference-limited environmentcharacterized by an interference component dominating noise (I>>N), itmay be possible to make a configuration as above because the noise isnegligible, although the power of a noise component, unlike theinterference component, cannot be reduced as much as the amountindicated by α.

The UE measures SINR based on the CSI processes 0, 1, and 2 configuredaccording to Tables 7 and 8 and transmits the measurement result to theeNB in the form of a CQI feedback. The eNB may acquire the relative SINRvalues X, Y, and Z of the eNBs A, B, and C based on the CQI feedbackfrom the UE and, if the SINR of the eNB A is acquired based on the SINRsof the three eNBs with the highest SRS-reception powers, apply B′=A*Y/Xfor eNB B and C′=B*Z/X for eNB C.

The signal strengths of the eNBs A, B, and C may be calculated asfollows with reference to Table 8.

$\begin{matrix}{{\frac{A}{\left( {A + B + C + {NI}} \right)/\alpha} = X},{A = \frac{NI}{{\left( {\alpha - Y - Z} \right)/X} - 1}}} & {{Equation}\mspace{14mu} 1} \\{{\frac{B}{\left( {A + B + C + {NI}} \right)/\alpha} = Y},{B = \frac{NI}{{\left( {\alpha - Z - X} \right)/Y} - 1}}} & {{Equation}\mspace{14mu} 2} \\{{\frac{C}{\left( {A + B + C + {NI}} \right)/\alpha} = Z},{C = \frac{NI}{{\left( {\alpha - X - Y} \right)/Z} - 1}}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

The eNB calculates the signal strengths of the eNBs A, B, and C from X,Y, and Z as SINR values based on the CQI feedback and substitutes themfor the SRS-reception powers at the eNBs A, B, and C. This gives gainsas follows. That is, in a carrier aggregation situation where theprimary cell (PCell) operates in both the uplink and downlink, it ispossible to calculate downlink SINR values for CoMP transmission basedon the SRS without any CSI process configuration. This is advantageousin terms of generating all available SINR combinations for CoMPtransmission of the eNBs having uplink SRS values; but, in FDD, it isnecessary to reduce performance degradation caused by channel conditionmismatch between downlink and uplink by reducing errors caused by theSRS values. Using the above-described CSI process configuration, it ispossible to acquire accurate downlink signal qualities for three eNBswith the highest SRS-reception powers so as to calculate the accurateSINR for CoMP transmission under the assumption of service from thethree eNBs with the highest SRS-reception powers and measure thestrengths of interference signals from the three eNBs with the highestSRS-reception powers under the assumption of service from other eNBs,resulting in improvement of total SINR estimation performance.

In a case where only the downlink exists, i.e., in a secondary cell(SCell) supporting no SRS transmission/reception in a carrieraggregation (CA) situation, it is impossible to use the same method asthe PCell because no SINR combination for CoMP transmission can begenerated based on SRS. In this case, the eNB and the UE may configurethe SINR per CoMP transmission scheme as follows using the CSI processconfigurations to the three eNBs with the highest SRS-reception powersacquired through the PCell.

$\begin{matrix}{{\frac{A}{NI} = \frac{1}{{\left( {\alpha - Y - Z} \right)/X} - 1}},{\frac{B}{NI} = \frac{1}{{\left( {\alpha - Z - X} \right)/Y} - 1}},{\frac{C}{NI} = \frac{1}{{\left( {\alpha - X - Y} \right)/Z} - 1}}} & {{Equation}\mspace{14mu} 4} \\{\frac{A}{B + C + {NI}} = {\frac{A/{NI}}{{B/{NI}} + {C/{NI}} + 1}\left( {{non}\mspace{14mu}{CoMP}} \right)}} & {{Equation}\mspace{14mu} 5} \\{\frac{A}{B + C + {NI}} = {\frac{A/{NI}}{{B/{NI}} + 1}\left( {{CS}/{CB}} \right)}} & {{Equation}\mspace{14mu} 6} \\{{\frac{A}{B + C + {NI}} = \frac{A/{NI}}{{B/{NI}} + {C/{NI}} + 1}},{\frac{B}{A + C + {NI}} = {\frac{B/{NI}}{{A/{NI}} + {C/{NI}} + 1}({DPS})}}} & {{Equation}\mspace{14mu} 7} \\{{J\;\frac{A + C}{B + {NI}}} - {\frac{{A/{NI}} + {C/{NI}}}{{B/{NI}} + 1}({JT})}} & {{Equation}\mspace{14mu} 8}\end{matrix}$

Equation (4) expresses relative signal strengths of the eNBs A, B, andC, and equations (5), (6), (7), and (8) are derived from equation (4).Equation (5) expresses a case where the eNB A is the serving eNB and thesignals from the eNBs B and C are regarded as interference components ina situation applying no CoMP transmission scheme. Equation (6) expressesa case where the eNB A transmits signals while the eNB C is not workingin a situation applying the CS/CB transmission scheme. Equation (7)expresses a case where the eNBs A and B transmit signals alternately.Equation (8) expresses a case where the eNBs A and C transmit signalssimultaneously in a situation applying the JT transmission scheme.

The operation difference between the SCell without SRS-reception powerand the PCell with SRS-reception power is that the SCell can configure aCoMP transmission scheme only for the three eNBs with the highestSRS-reception powers in association with the PCell. As described above,the PCell is capable of configuring a CoMP transmission scheme for morethan 3 eNBs by substituting the downlink signal strengths calculatedbased on the CQI feedback for the SRS-reception power for the 3 eNBswith the highest SRS-reception powers and applying the SRS-receptionpowers for the eNBs with the non-highest SRS-reception powers.

The operation of the present invention may be performed by the twodevices of FIGS. 7 and 8. FIG. 7 is a block diagram illustrating an eNBcontrolling the CoMP transmission operation, and FIG. 8 is a blockdiagram illustrating an eNB and a CoMP management unit that isimplemented as a separate device for controlling the CoMP transmissionoperation.

In reference to FIG. 7, an SRS reception unit 710 receives an SRStransmitted by a UE 700, and a CoMP management unit/SRS reception powerstorage unit 730 performs all calculations related to CoMP transmissionoperations including determining a CoMP transmission scheme to beperformed with neighboring eNBs based on the SRS-reception powerinformation received from the neighboring eNB 770, SRS-reception powerinformation received from the SRS reception unit 710, and data receivedfrom a buffer management unit 720 and transmits information on thecandidate CoMP eNBs for performing the CoMP transmission to aCSI-RS/CSI-IM/CSI process configuration unit 740. Here, the CoMPtransmission operation is determined through negotiation and informationexchange with the neighboring eNBs. The neighboring eNB may be a logicalentity existing in the same hardware or a physically-separated eNB. TheCSI-RS/CSI-IM/CSI process configuration unit 740 configuresCSI-RS/CSI-IM/CSI processes based on the information of the eNBsparticipating the CoMP transmission that is provided by the CoMPmanagement unit according to an embodiment of the present invention andtransmits the configuration information to the UE and a channel qualityreference value generation unit 750. The channel quality reference valuegeneration unit generates SINR information for downlink datatransmission in a CoMP transmission scheme, receives channel qualityinformation from the UE through CSI processes, and transmits a channelquality reference value to an MCS determination unit 760. The MCSdetermination unit determines an MCS and notifies a modem of the MCS.The buffer management unit 720 determines presence/absence of user data,manages UEs having data to transmit thereto and buffer size, andtransmits buffer information to the CoMP management unit/SRS receptionpower storage unit. The buffer management unit, the SRS reception unit,the CoMP management unit/SRS reception power storage unit, theCSI-RS/CSI-IM/CSI process configuration unit, the channel qualityreference value generation unit, and the MCS determination unit may belocated inside the eNB 780, transmit/receive signals to/from the UE andthe neighboring eNB by means of a transceiver, and be configured in sucha way that the management unit includes the buffer management unit, theCoMP management unit, the CSI-RS/CSI-IM/CSI process configuration unit,the channel quality reference value generation unit, and the MCSconfiguration unit.

In reference to FIG. 8, the eNB 870 may include a buffer management unit820, an SRS reception unit 810, a CSI-RS/CSI-IM/CSI processconfiguration unit 830, a channel quality reference value generationunit 840, and an MCS determination unit 850; a CoMP management unit/SRSreception power storage unit 860 may be implemented as a separate device880 outside the eNB, and the CoMP management unit may receive CoMPoperation-related information transmitted by individual eNBs, manage andnotify the CoMP scheme to be used by the eNB, candidate eNB information,and SRS reception power based on the CoMP operation-related informationin a centralized manner. A separate device for managing eNBs and CoMPschemes may include a transceiver and a management unit, and thetransceiver may communicate signals with the UE and neighboring eNBs,the management unit may include the buffer management unit, theCSI-RS/CSI-IM/CSI process configuration unit, the channel qualityreference value generation unit, and the MCS determination unit, and themanagement unit of the separate device may include the CoMP managementunit/SRS reception power storage unit.

It is to be appreciated that those skilled in the art can change ormodify the embodiments without departing from the technical concept ofthis invention. Accordingly, it should be understood that theabove-described embodiments are essentially for illustrative purposesonly and are not in any way for restriction thereto. Thus, the scope ofthe invention should be determined by the appended claims and theirlegal equivalents rather than the specification, and various alterationsand modifications within the definition and scope of the claims areincluded in the claims.

Although various embodiments of the present invention have beendescribed using specific terms, the specification and drawings are to beregarded in an illustrative rather than a restrictive sense in order tohelp understand the present invention. It is obvious to those skilled inthe art that various modifications and changes can be made theretowithout departing from the broader spirit and scope of the invention.

What is claimed is:
 1. A method by a terminal in a wirelesscommunication system, the method comprising: transmitting an uplinksounding reference signal to a plurality of base stations, including aserving transmission point and neighboring transmission points, whereinthe serving transmission point serves the terminal and the neighboringtransmission points are neighbors to the serving transmission point;receiving channel status information (CSI) configuration informationincluding CSI process configurations configured for measuring downlinktransmission powers of N transmission points from among the servingtransmission point and the neighboring transmission points, wherein theN transmission points are selected as the N transmission points havinghighest reception powers of the sounding reference signal among theserving transmission point and the neighboring transmission points,based on a result of ordering the reception powers of the soundingreference signal received by each of the serving transmission point andthe neighboring transmission points from highest to lowest receptionpower based on a comparison of the reception powers of the soundingreference signal; measuring a signal-to-interference-plus-noise ratiobased on the CSI configuration information; generating channel qualityinformation (CQI) based on the signal-to-interference-plus-noise ratio;and transmitting the CQI to the serving transmission point.
 2. Themethod of claim 1, wherein the CSI configuration information furtherincludes CSI interference measurement configurations, and wherein theCSI interference measurement configurations comprise one CSIinterference measurement configuration which is configured for measuringtransmission powers of all of the serving and neighboring transmissionpoints.
 3. The method of claim 1, wherein the CSI process configurationscomprise N CSI process configurations as combinations of CSI referencesignal configurations and CSI interference measurement configurations.4. The method of claim 1, further comprising receiving data transmittedusing a Modulation and Coding Scheme (MCS) determined based on the CQI.5. A method by a base station including a serving transmission point andneighboring transmission points in a wireless communication system, themethod comprising: receiving an uplink sounding reference signal from aterminal; identifying a reception power of the sounding reference signalreceived at each of the serving transmission point and the neighboringtransmission points, wherein the serving transmission point serves theterminal and the neighboring transmission points are neighbors to theserving transmission point; selecting N transmission points havinghighest reception powers of the sounding reference signal from among theserving transmission point and the neighboring transmission points,based on ordering the reception powers of the sounding reference signalreceived by each of the serving transmission point and neighboringtransmission points from highest to lowest reception power based on acomparison of the reception powers of the sounding reference signal;generating channel status information (CSI) configuration informationincluding CSI process configurations configured for measuring downlinktransmission powers of the selected N transmission points; transmittingthe CSI configuration information to the terminal; and receiving channelquality information (CQI) from the terminal, the CQI being generated bythe terminal based on a signal-to-interference-plus-noise ratio measuredby the terminal based on the CSI configuration information.
 6. Themethod of claim 5, wherein the CSI configuration information furtherincludes CSI interference measurement configurations, and wherein theCSI interference measurement configurations comprise one CSIinterference measurement configuration which is configured for measuringtransmission signal powers of all of the serving transmission point andthe neighboring transmission points.
 7. The method of claim 5, whereinthe CSI process configurations comprise N CSI process configurations ascombinations of CSI reference signal configurations and CSI interferencemeasurement configurations.
 8. The method of claim 5, further comprisingtransmitting data using a Modulation and Coding Scheme (MCS) determinedbased on the CQI.
 9. A terminal in a wireless communication system, theterminal comprising: a transceiver; and a controller configured tocontrol the transceiver to: transmit an uplink sounding reference signalto a plurality of base stations that includes a serving transmissionpoint and neighboring transmission points, wherein the servingtransmission point serves the terminal and the neighboring transmissionpoints are neighbors to the serving transmission point, receive channelstatus information (CSI) configuration information including CSI processconfigurations configured for measuring downlink transmission powers ofN transmission points from among the serving transmission point and theneighboring transmission points, wherein the N transmission points areselected as the N transmission points having highest reception powers ofthe sounding reference signal among the serving transmission point andthe neighboring transmission points, based on a result of ordering thereception powers of the sounding reference signal received by each ofthe serving transmission point and the neighboring transmission pointsfrom highest to lowest reception power based on a comparison of thereception powers of the sounding reference signal, measure asignal-to-interference-plus-noise ratio based on the CSI configurationinformation; generate channel quality information (CQI) based on thesignal-to-interference-plus-noise ratio; and transmit the CQI to theserving transmission point.
 10. The terminal of claim 9, wherein the CSIconfiguration information further includes CSI interference measurementconfigurations, and wherein the CSI interference measurementconfigurations comprise one CSI interference measurement configurationwhich is configured for measuring transmission signal powers of all ofthe serving transmission point and the neighboring transmission points.11. The terminal of claim 9, wherein the CSI process configurationscomprise N CSI process configurations as combinations of CSI referencesignal configurations and CSI interference measurement configurations.12. The terminal of claim 9, wherein the controller controls thetransceiver to receive data transmitted using a Modulation and CodingScheme (MCS) determined based on the CQI.
 13. A base station of aplurality of base stations including a serving transmission point andneighboring transmission points in a wireless communication system, thebase station comprising: a transceiver; and a controller configured to:control the transceiver to receive an uplink sounding reference signalfrom a terminal, identify a reception power of the sounding referencesignal received at each of the serving transmission point and theneighboring transmission points, wherein the serving transmission pointserves the terminal and the neighboring transmission points areneighbors to the serving transmission point, select N transmissionpoints having highest reception powers of the sounding reference signalfrom among the serving transmission point and the neighboringtransmission points, based on ordering the reception powers of thesounding reference signal received by each of the serving transmissionpoint and neighboring transmission points from highest to lowestreception power based on a comparison of the reception powers of thesounding reference signal, generate channel status information (CSI)configuration information including CSI process configurationsconfigured for measuring downlink transmission powers of the selected Ntransmission points, control the transceiver to transmit CSIconfiguration information to the terminal, and control the transceiverto receive channel quality information (CQI) from the terminal, the CQIbeing generated by the terminal based on asignal-to-interference-plus-noise ratio measured by the terminal basedon the CSI configuration information.
 14. The base station of claim 13,wherein the CSI configuration information further includes CSIinterference measurement configurations, and wherein the controllerconfigures one CSI interference measurement configuration which isconfigured for measuring transmission signal powers of all of theserving transmission point and the neighboring transmission points. 15.The base station of claim 13, wherein the controller configures N CSIprocess configurations as combinations of CSI reference signalconfigurations and CSI interference measurement configurations.
 16. Thebase station of claim 13, wherein the controller controls thetransceiver to transmit data using a Modulation and Coding Scheme (MCS)determined based on the CQI.